Video consumption is spreading across three main platforms—TV, Internet, and mobile—instead of concentrating in just one area, according to a new “Three Screen Report” by market analyzer Nielsen.

As affirmed by many other reports, Nielsen has concluded that online video is continuing to show healthy growth. With videos on the most popular video sharing site on the Web, YouTube, being limited to durations of ten minutes or less, short clips remain the most commonly watched videos online. Nielsen says that, in May of this year, these shorter videos made up 83% of online video viewing.

Mobile video viewing shows no signs of slowing, as 15 million Americans reported watching mobile video in Q2 2009—a 70% increase over the year before. In contrast to online viewing trends, mobile viewing is made up mostly of TV network content.

Significantly, online entertainment is a long way from dethroning the king of video: television. In a country where the average home has 2.5 people and 2.86 TV sets, according to Nielsen, it is unsurprising to see that TV viewing remains at all-time highs: in the second quarter of this year, users watched, on average, over 140 hours of television per month.

TV likely supports these high watch rates with new technologies popular with consumers, like timeshifted television. Nielsen reports that nearly 1 in 3 U.S. homes have DVR devices and predicts that the devices will only become more popular in the future.

If TV viewing is growing, online video is growing, and mobile video is growing, where are Americans finding all the extra time?

Nielsen concludes that Americans are rapidly becoming virtuosos at multi-tasking their media intake. According to the report, over half of the homes equipped with Internet and TV use both simultaneously at least once a month. Statistics gathered in June say that 28% of time online is shared with TV viewing. Alternately, only 3% of TV viewing time is shared with Internet usage.

Nevertheless, Nielsen sees a rising tide of consumers who plug into multiple mediums at once for their content instead of total concentration in any one device or network. Americans now consume their media on three main fronts: TV, Internet, and mobile.